Polimorfismo em Óxidos: Um Estudo de Primeiros Princípios das Fases Trigonal e Monoclínica do Al2O3

Abstract

Among ceramic oxides, aluminum oxide (Al2O3) stands out as one of the most important materials for advanced technological applications, especially in the aerospace sector, due to its high thermal stability, chemical resistance, dielectric properties, and favorable optical behavior. This material exhibits a very rich polymorphism, with different crystalline phases coexisting or transforming depending on thermodynamic and kinetic conditions, which leads to distinct physical properties. The trigonal phase (α-Al2O3, corundum) is well characterized and widely used in severe applications; however, less-studied phases, such as the monoclinic one, still lack systematic investigations that relate crystal structure to fundamental properties. In this work, the trigonal and monoclinic phases of Al2O3 are investigated using first-principles methods based on Density Functional Theory (DFT), employing different exchange–correlation functional approximations. Structural, electronic, optical, and thermodynamic properties are analyzed, including lattice parameters, electronic density of states, dielectric functions, optical absorption spectra, enthalpy, entropy, and free energy, in order to understand how polymorphism influences the physical behavior of the material. The results show that the trigonal phase is thermodynamically the most stable over a wide temperature range, exhibits high structural rigidity, and presents optical behavior consistent with its established use in thermal protection systems and structural components. In contrast, the monoclinic phase displays distinct optical and dielectric properties due to its lower crystal symmetry and greater vibrational complexity, which suggests emerging potential for applications in aerospace environments, such as selective coatings, dielectric components, optical filters, and devices operating under intense radiation and extreme temperature conditions. In addition, a scientometric analysis of publications on Al2O3 is carried out based on the Scopus and Web of Science databases to map the evolution of studies, research trends, leading research centers, and expanding application areas. The growth of scientific interest in the functional properties of alumina, evidenced by this analysis, reinforces the current relevance of studies devoted to polymorphism and to less-explored phases. Thus, this work advances the understanding of the interrelationship between crystal structure and the physical properties of Al2O3, providing a robust theoretical foundation that can be exploited in the search for new aerospace applications, particularly with regard to the monoclinic phase, while also indicating promising directions for future investigations involving mechanical and vibrational properties and experimental validation.